This application claims the priorities of Korean Patent Application No. 2002-10527 filed on Feb. 27, 2002, Korean Patent Application No. 2002-78674 filed on Dec. 11, 2002, and Korean Patent Application No. 2003-10377 filed on Feb. 19, 2003, in the Korean Intellectual Property Office, the disclosure of which, is incorporated herein in their entirety by reference.
1. Field of the Invention
The present invention relates to a vaned spool type directional control valve and a four-way reversible valve for a cooling cycle system using the same, and more particularly, to a directional control valve having a spool with a vane incorporated therein and operated in an internal or external pilot method, in which a pilot valve for the operation of the spool is incorporated into a valve main body, and to an application of the same which can be used as a solenoid-pilot operated control valve.
2. Description of the Related Art
A valve changing or stopping the direction of motion of an actuator such as an air cylinder or an oil hydraulic motor in an air pressure or oil hydraulic circuit is referred to as a directional control valve or simply a control valve. According to the type of a spool, the directional control valve is classified into a rotary spool type in which a spool rotates around an axis and a slide spool type in which a spool reciprocates along an axial direction. Also, according to the operation type of the spool, the directional control valve is classified into a manual type in which a spool is directly manipulated using a lever or handle, a mechanical type in which a spool is engaged by a moving cam, a solenoid type using a solenoid thrust of a solenoid, a pilot operated type using compressed air or oil, and an solenoid pilot operated type in which the solenoid type and the pilot operated type are combined.
Among the above various types, the solenoid type is easy to control in a remote control, automatic control, and emergency stop. However, since the solenoid type directly moves the spool by thrust of a solenoid, a solenoid having a large capacity is needed for the change of motion of a large amount of fluid. In contrast, the pilot operated type can change the flow of a large amount of fluid in a main circuit using the same pressure necessary to change the flow of a small amount of fluid. Thus, the solenoid-pilot operated control type combining the solenoid type and the pilot operated type is easy to control and capable of changing the flow of a large amount of fluid with a small solenoid so that it is one of directional control valves most widely used. The pilot method of the solenoid-pilot operated control type is classified into an external pilot type taking fluid from an additional circuit not a main circuit and an internal pilot type taking fluid from the main circuit. The internal pilot type is mainly adopted. The solenoid-pilot operated control type is disclosed in U.S. Pat. Nos. 4,150,695, 4,245,671, 6,192,937, and 6,325,102. According to these patents, a conventional solenoid-pilot operated control valve is made of a combination of a separated solenoid control type and a pilot operated control type. That is, the solenoid control valve is used as a pilot valve and the pilot operated control valve is used a as main valve. Also, the main valve is usually a slide spool type.
Meanwhile, U.S. Pat. Nos. 4,469,134 and 4,492,252 disclose a four-way reversible valve, as a sort of a solenoid-pilot control valve, used for a cooling cycle system such as a heating/cooling heat pump air conditioner. The principle and structure of the four-way reversible valve are the same as those used for a common air pressure or oil hydraulic circuit, but different in that a metal casing considering an environment of a high temperature and high pressure two-phase refrigerant is used and the casing is connected to a circuit by welding a refrigerant pipe thereto.
As is well known, the cooling/heating heat pump air conditioner has a mechanism of transfer of heat during the cycle of compression-condensation-expansion-evaporation of refrigerant. Cool airflow needed for cooling and hot airflow needed for heating are generated through heat exchange during the condensation and evaporation cycles. The cooling operation and heating operation is selected by switching the positions of heat exchangers, that is, a condenser and an evaporator, respectively used in the condensation and evaporation cycles. However, since the switch of the positions of the condenser and the evaporator is practically impossible, the flow of refrigerant in the condenser and the evaporator is changed by using a four-way reversible valve which is one of directional control valves.
The rotary spool type of the directional control valves is typically difficult to control because pressure on a circumference of a spool is not balanced and a lateral pressure increases under a high pressure. Thus, the rotary spool type is not appropriate for a high pressure use. Also, since the changing speed in the rotary spool type is slow and the rotary spool type is appropriate for a manual type, the application of the rotary spool type is limited.
The slide spool type is advantageous in that, compared to the rotary spool type, pressure is well balanced and the lateral pressure applied to the spool is small so that the switching is easily and quickly performed and pressure being used is high. However, since a lot of valve members are needed due to the structure of the slide spool and a gap between each valve member and a body is generated, affecting the leakage of liquid, so that a fine process is needed. This is because the valve body of a slide spool type is manufactured in a complicated post-processes after aluminum die casting so that manufacture thereof is difficult and the cost is high.
The solenoid-pilot control valve which has been frequently used is a slide spool type and has a structure of coupling a separate pilot valve to a main valve using a bolt. Accordingly, since seal to prevent leakage between valves and valve members such as a piston head to transfer the pressure of fluid by the pilot valve are added, the number of leakage points increases accordingly and malfunction is frequent so that the cost of the valve increases, which prevents supply of the valve at a low cost.
Also, the conventional slide spool type solenoid-pilot control valve has a structure in which a solenoid is connected in the axial direction of the spool so that the entire length of the valve increases and a large space is required. This problem is highlighted in a dual solenoid type.
Meanwhile, in the four-way reversible valve which is a sort of a solenoid-pilot control valve, in order to connect a pilot valve to a main valve in an internal pilot type, the four-way reversible valve is not directly connected and an additional capillary tube is additionally welded. That is, manufacture of the valve is difficult due to numerous welding points and the number of defective valves due to welding increases.